body{
  margin: 0;
  background: rgba(0,0,0,.5);
}
.wrapper{
  width: 500px;
  height: 400px;
  background: #fff;

  /*水平垂直居中*/
  position: absolute;
  left: 50%;
  top: 50%;
  margin-left: -250px;
  margin-top: -200px;
  border-radius: 10px;

  overflow: hidden;
}
.main{
  width: 100%;
  height: 100%;
}
.main .bg{
  width: 100%;
}
.content{
  position: relative;
  border-bottom: 1px solid #ccc;
  margin-top: 50px;
  height: 50px;
  text-align: center;
  line-height: 50px;
  font-size: 20px;
}
.content span{
  position: absolute;
  top: 0;
  width: 200px;
  text-align: center;
  height: 50px;
  transition: left .3s linear ;
}
/*nth-child()*/
/*nth-of-type()*/
.content .state1{
  left: 0;
}
.content .state2{
  left: 300px;
}
.btn{
  position: relative;
  z-index: 10;
  width: 30px;
  height: 30px;
  background-image: url("../images/change.png") ;
  background-size: 100% 100%;
  transition: transform 0.3s linear;

  display: inline-block;
  vertical-align: middle;

  /*position: absolute;*/
  /*top: 50%;*/
  /*left: 50%;*/
  /*margin-left: -15px;*/
  /*margin-top: -15px ;*/
}

.card{
  position: absolute;
  z-index: 20;
  left: 100%;
  top: 0;
  width: 100%;
  height: 100%;
  background: #fff;
  border-radius: 10px;
  transition: left .3s linear;
}
.return{
  font-size: 12px;
  color: #cccccc;
  display: inline-block;
  margin: 10px 0 0 20px;
}
h2 {
  text-align: center;
}
ul{
  padding: 0;
  /*margin: 0;*/
  width: 80%;
  margin: 0 auto;
}
li{
  display: inline-block;
  margin: 7px;
  list-style: none;
  width: 15%;
  height: 40px;
  text-align: center;
  line-height: 40px;
  border-radius: 10px;
  border: 1px solid #ccc;
}
li:hover{
  color: orangered;
}